1. Field of the Invention
The invention is generally related to polymer alloys and their applications. Particularly, the invention is directed to making polymer alloys with high heat storage capacity within room temperature and adequate engineering attributes for use in building construction.
2. Description of the Relevant Art
Polymer blending has been subject of major efforts to develop new polymers of modified properties. U.S. Pat. No. 5,614,305 to Lavengood et al. discloses a blend of nylon with rubber with higher levels of impact resistance than nylon can provide. U.S. Pat. No. 4,954,546 to Abeler et al. discloses a blend of PVC with lauriltin compounds which provides improved stability upon prolonged exposure to light and heat. U.S. Pat. No. 5,055,525 discloses polymer blend compositions with improved toughness characteristics. U.S. Pat. No. 5,194,494 to Henton et al. discloses polymer blend compositions with improved resistance to heat. U.S. Pat. No. 5,391,622 to Ho et al. discloses polymer blends which exhibit high levels of electrical conductivity.
The above inventions are examples of those seeking to develop polymer blends with new combinations of properties. The polymer blend which is subject of this application is distinguished from all past inventions by the presence of thermoplastics of relatively low melt temperature (say, within the comfort range of room temperature) in the blend; said thermoplastics are absorb relatively large quantities of latent heat in the vicinity of their melt temperature. However, said thermoplastics have limited serviceability, because they soften and melt within room temperature. We have discovered that blending of said thermoplastics with thermosets or high-temperature thermoplastics can yield polymer blends with relatively high levels of strength and stiffness within room temperature (and even at elevated temperatures), where the low-melt-temperature thermoplastics still absorbs relatively large quantities of latent heat. Absorption of latent heat in said polymer blends is not accompanied with major loss of mechanical properties. Such novel polymer blends can be used in energy-efficient building construction, and also can find broader applications involving storage of excess heat.
It is an object of this invention to develop a polymer alloy with desirable physical and mechanical characteristics and relatively high heat storage capacity, that includes at least one low-melt-temperature thermoplastic capable of latent heat storage within the service temperature range and at least one thermoset (or high-melt temperature thermoplastic, or elastomer) to provide the blend with desirable physical and mechanical characteristics.
It is another object of this invention to develop polymer composites of desirable physical and mechanical characteristics and relatively high heat storage capacity, with at least one of fillers and fibers embedded within a polymer alloy that includes at least one low-melt-temperature thermoplastic capable of latent heat storage within the service temperature range.
It is another object of this invention to develop polymer alloys and composites with relatively high heat storage capacity, that remain solid within the service temperature range.
Applicant has discovered that low-melt-temperature thermoplastics, when blended with thermosets (or high-melt-temperature thermoplastics, or elastomers) can provide their latent heat storage capacity while the alloy remains solid in the vicinity of the melt temperature of said low-melt-temperature thermoplastic. Addition of fillers and reinforcement with fibers can enhance the physical and mechanical characteristics of the polymer alloy within the service range of temperature and also at elevated temperatures.
According to the invention, there is provided a polymer alloy where at least one low-melt-temperature thermoplastic provides relatively large latent heat storage capacity within the service range of temperature, and at least one of thermosets, high-melt-temperature thermoplastics, and elasomers are used in the alloy to ensure that the whole blend remains solid and provides desirable physical and mechanical characteristics within the service range of temperature. The polymer alloy can be refined through the addition of fillers, fibers, and other additives.
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Most materials store relatively small quantities of heat through temperature rise without phase change, and store relatively large quantities of (latent) heat with a relatively small temperature rise once they undergo phase change (e.g., melting). There are many applications where heat storage capacity of materials is an important design criterion. For example, materials capable of storage of relatively high quantities of heat within the comfort range of room temperature can benefit the energy-efficiency of buildings. There are also many electrical and mechanical applications where excess heat has to be removed (e.g., stored in other materials) within a certain temperature range in order to avoid over-heating.
Thermoplastics provide diverse melt temperatures. During melting, however, thermoplastics cease to retain the desirable physical and mechanical characteristics associated with the solid phase (e.g., strength and stiffness), and thus fail to meet such basic serviceability requirements as the ability to support or contain. The relatively high latent heat storage capacity of thermoplastics is therefore accompanied with loss of serviceability (stiffness, strength, etc.).
Applicant has discovered that blending of thermplastics of low melt temperature with thermosets (or high-melt-temperature thermoplastics, or elastomers) can yield a polymer alloy in which the low-melt-temperature thermoplastic provides its relatively high latent heat storage capacity while the thermoset (or high-melt-temperature thermoplastic, or elastomer) prevents the whole blend from melting or major loss of physical and mechanical characteristics as the melt temperature of the low-melt-temperature thermoplastic is exceeded. This polymer alloy can be modified by the addition of fillers, fibers, fire-retardants, compatibilisers, and other additives in order to tailor certain aspects of its processing and/or performance characteristics.
Different low-melt-temperautre thermoplastics, including polyethylene glycol, polycaprolactone triol, polycaprolactone diol, polyvinyl acetate, polybutyl methacrylate, poly n-butyl methacrylate, polylaurylactone, and polymethyl methacrylate can be used in the polymer alloys for latent heat storage within the service temperature of particular applications. In the case of applications with elevated service temperature, one can use thermoplastics such as acrylics and (thermoplastic) polyesters for the purpose of latent heat absorption.
Different thermosets, including epoxies, polyesters, phenolics, silicones, urethanes and urea melamine can be used in conjunction with the low-melt-temperature thermoplastics in the polymer alloys. Elastomers such as natural rubbers, polyisoprenes, neoprenes, polysiloxanes, diisocyanate polyesters, and butadiene-styrene copolymers can also be used in conjunction with low-melt-temperature thermoplastics. Depending on the service temperature of particular applications, one can also use higher-melt-temperature thermoplastics such as acetals, cellulosics, and polycarbonates in conjunction with lower-melt-temperature thermoplastics.
When at least one of thermosets, elastomers and higher-melt-temperature thermoplastics are blended with low-melt-temperature thermoplastics, the resulting polymer alloy retains the relatively high latent heat storage capacity of the low-melt-temperature themoplastics, with the alloy remaining solid as the melt temperature of the low-melt-temperature thermoplastic is exceeded. The alloy is therefore capable of substantial latent heat storage while remaining solid upon temperature rise.
Alloys of low-melt-temperature thermoplastics with at least one of thermosets, elastomers and high-melt-temperature thermoplastics can be modified by the addition of fillers, fibers, fire retardants, compatibilisers, and other additives. The polymer alloys can also be subjected to different processing techniques suiting polymers and polymer composites, including compression molding, bulk molding, filament winding, hand lay-up, injection molding, pultrusion, extrusion, reaction injection molding, resin transfer molding, sheet molding, and spray deposition.